Drilling device for earth drill

ABSTRACT

Locking elements  3   d  and  3   j  are provided at an inner member  3  connected to a kelly bar  1 , and a locking element bearing plate  6   f is provided at an outer member  6 . The outer member  6  includes a cylindrical bucket  7  and a grab bucket  8  housed inside the cylindrical bucket  7 . When an excavating tool  2  is in its most contracted state, the inner member  3  is rotated forward to lock the locking elements  3   d  and  3   j  at the locking element bearing plate  6   f , thereby disallowing relative vertical movement of the inner member  3  and the outer member  6 . As the excavating tool is rotated by applying a force to the kelly bar  1  along the lifting direction in this state, an excavating operation can be executed while applying a load smaller than the load of the excavating tool  2 . As a result, it becomes possible to execute an excavating operation with a large excavating tool in conjunction with an earth drill having a small drive force. Projections  3   k  provided at the outer circumference of the inner member  3  are fitted at guide rails extending along the longitudinal direction and provided at the inner circumference of the second member  5  so as to be allowed to move up/down freely. Thus, the grab bucket  8  having an underground obstacle grabbed therein can be rotated to remove the underground obstacle.

TECHNICAL FIELD

[0001] The present invention relates to an excavating tool mounted atthe kelly bar of an earth drill to excavate cobblestones, boulders,concrete slab or the like.

BACKGROUND ART

[0002] An earth drill, which excavates material by taking in excavatedsoil into a bucket while excavating the bottom of a bore hole with acutter provided at a conical bottom cover, is normally ideal for anexcavating operation on a soil stratum that can be represented with an Nvalue. However, it is not suited for so-called barrier excavationincluding excavation of stones such as cobblestones and boulders thatare too large to fit into the drilling bucket and excavation of aconcrete slab. If the cutter strikes such a layer during an excavatingoperation, special measures must be taken by, for instance, removing thecobblestones with a hammer grab bucket mounted at a separate crane orusing an all casing machine.

[0003] The inventor of the present invention et al. proposed in JapaneseUnexamined Patent Publication No. H 11-141261 a means for solving theproblem described above, achieved by mounting a detachable cylindricalbucket at the kelly bar instead of the drilling bucket for the earthdrill having the bottom cover and by also providing a auger typeexcavating tool that forms a small hole in the vicinity of its circulardrilling groove to allow excavated material to be drawn out through thehole.

[0004] However, there is a problem with an earth drill that utilizes acylindrical bucket as disclosed in Japanese Unexamined PatentPublication No. H 11-141261 in that a separate lifting means is requiredto lift the excavated round slab, rocks and the like.

[0005] Accordingly, the inventor of the present invention et al.proposed an excavating tool for an earth drill in Japanese UnexaminedPatent Publication No. 2001-90465, which allows excavated material to belifted to the ground level during a barrier excavating operation ofslab, cobblestones, boulders or the like executed with the earth drill.

[0006] The excavating tool disclosed in the publication described abovecomprises an inner member having an upper end thereof connected to thekelly bar, an outer member and a second member provided between theinner member and the outer member. These members are combined so as toallow them to move up/down relative to one another. In addition, acylindrical bracket having an cutting teeth at the lower end thereof andan open bottom is mounted at the outer member. At the outer member, agrab bucket housed inside the cylindrical bucket and constituted of apair of jaws which grab objects excavated with the cylindrical bucket isprovided as well.

[0007] The lower end of the second member is linked to the jaws at thegrab bucket so as to open and close the grab bucket. The excavating tooladopts a structure that closes the grab bucket as the second membermoves upward relative to the outer member and opens the grab bucket asthe second member moves downward relative to the outer member. Namely,the inner member and the second member are connected with each otherthrough a first hydraulic cylinder and second hydraulic cylindersprovided between the second member and the grab bucket. Pressure isgenerated as the kelly bar is lifted and the first hydraulic cylinderconsequently extends, which communicates the pressure to the secondhydraulic cylinders to extend the second hydraulic cylinder. This liftsthe second member relative to the outer member, and thus, the grabbucket mounted at the outer member closes to trap soil.

[0008] The excavating tool adopts a structure that automaticallyreleases the binds among the inner member, the second member and theouter member achieved with cotters to allow them to extend as themembers held in a most contained state achieved with the cotters arelowered to the bottom of the bore hole. Then, as the kelly bar isrotated, the cylindrical bucket and the grab bucket are caused to rotatetogether with the inner member, the second member and the outer memberto cut into the earth. When the kelly bar is lifted after the earth iscut to a predetermined depth, the inner member is lifted together withthe kelly bar while the outer member remains at the bottom of the borehole due to the dead weight of the cylindrical bucket, the grab bucketand the like. As a result, the grab bucket, with its jaws linked to thesecond member, closes through the operation described above to take inthe soil to be excavated. After the grab bucket is closed, the outermember is lifted to the ground level together with the cylindricalbucket and the grab bucket. As the cylindrical bucket is set on theground and the kelly bar is lowered, the first hydraulic cylindercontracts, the pressure generated in the pressure oil through thecontraction of the first hydraulic cylinder causes the second hydrauliccylinders to contract as well and the second member is lowered as aresult, thereby allowing the grab bucket to open to discharge theexcavated soil onto the ground.

DISCLOSURE OF THE INVENTION

[0009] The excavating tool for an earth drill disclosed in JapaneseUnexamined Patent Publication No. 2001-90465 described above is yet toaddress the following problems.

[0010] (1) This excavating tool executes excavation while a loadrepresenting the sum of the dead weight of the excavating tool and thepressing force of the kelly bar achieved by setting the cylindricalbucket on the excavating surface in a state in which the grab bucket isopen and then by pushing down the kelly bar. However, the level of theload that can be applied to the excavating surface while the grab bucketis open becomes equal to or greater than the load of the excavating tooland thus, the pressing force constituted of a load less than that of theexcavating tool cannot be applied. To explain this in more specificterms, as the excavating tool is lowered to the bottom of the bore hole,the cotter mounted at the outer member becomes automatically disengagedfrom the hole of the second member and the hole of the inner member, andif the kelly bar is lifted in this state, the inner member becomes alsolifted relative to the second member and the second member, too, becomeslifted relative to the outer member, thereby closing the grab bucket.

[0011] For this reason, the excavating operation may become difficult ifan earth drill with a small drive force is utilized to rotate acylindrical bucket with a large diameter, since a large excavatingtorque is required due to the increase in the resistance at theexcavating surface, the dead weight of the large excavating tool and thelike.

[0012] (2) In addition, since the pressing force cannot be controlled soas not to exceed the dead weight of the excavating tool, the cuttermounted at the lower end of the outer member may become damaged readily.

[0013] (3) Japanese Unexamined Patent Publication No. 2001-90465described above discloses in one of the embodiments a structure detailedbelow. Namely, in a state in which the excavating tool is at its mostcontracted, a projection formed at the outer circumference of the innermember becomes engaged at a notch formed at the sleeve of the secondmember, thereby preventing the relative vertical movement among themembers so as to allow the grab bucket to be lifted while it is open.However, there is a problem with this structure in that if there is arelatively large underground obstacle such as a rock, the undergroundobstacle cannot be removed by closing the jaws to a certain extent androtating the underground obstacle grabbed with the jaws.

[0014] An object of the present invention is to provide an excavatingtool for an earth drill having a cylindrical bucket with a grab bucketprovided therein which is closed by using the force with which the kellybar is lifted, which allows an excavating operation to be executed whilea load smaller than the load of the excavating tool is applied, therebyenabling an earth drill with a small drive force to excavate materialwith a relatively large excavating tool and makes it possible to removeunderground obstacles by rotating the grab bucket in a state in whichthe grab bucket is partially closed.

[0015] (1) In order to achieve the object described above, theexcavating tool for an earth drill according to the present inventioncomprises a tubular inner member linked to the kelly bar, a tubularsecond member fitted on the outer side of the inner member so as to beallowed to move up/down freely and an outer member should on the outerside of the second member so as to be allowed to move up/down. Acylindrical bucket and a grab bucket housed inside the cylindricalbucket are mounted at the outer member, a first hydraulic cylinder ismounted between the inner member and the second member, second hydrauliccylinders which are caused to extend or contract by pressure oil fromthe first hydraulic cylinder are mounted between the second member andthe jaws of the grab bucket, and a locking mechanism is provided betweenthe inner member and the outer member. The locking mechanism isconstituted of a locking element provided at the outer circumference ofthe inner member and a locking element bearing plate provided at the topof the outer member, the locking element is allowed to pass through thelocking element bearing plate when the inner member and the outer memberachieve a specific relative rotational angle, and the locking element islocked at the locking element bearing plate to disallow relativevertical movement of the inner member and the outer member as the innermember is rotated along the forward direction when the excavating toolis in the most contracted state. A projection provided at the outercircumference of the inner member is fitted in guide rails providedalong the longitudinal direction at the inner circumference of thesecond member so as to be allowed to move up/down freely, and the innermember is allowed to rotate forward over a predetermined range relativeto the second member when the excavating tool is in the most contractedstate.

[0016] Since the locking mechanism that disallows the relative verticalmovement of the inner member and the outer member when the excavatingtool is in the most contracted state is provided as described above, anexcavating operation can be executed while a load smaller than the loadof the excavating tool is applied by the cylindrical bucket to theexcavating surface by applying a certain level of force to the kelly baralong the lifting direction to rotate the kelly bar along the forwardrotating direction, i.e., along the excavating direction. As a result,even when excavating material by using a small earth drill torotationally drive a relatively large excavating tool, a sufficientdrive force is assured for the excavating operation. In addition, theexcavating operation can be executed in an optimal manner with a smallpressing force as called for in specific individual situations.

[0017] Furthermore, even if there is an excessively large liftingreactive force when the grab bucket is operated along the closingdirection at the bottom of the bore hole, the grab bucket can still belifted in an open state by lowering the inner member again, rotating thekelly bar by a predetermined angle along the forward direction andlocking the locking element at the locking element bearing plate. Thus,the risk of not being able to lift the excavating tool out of the groundunder such circumstances is eliminated.

[0018] Since the second member and the outer member can be caused torotate reciprocally by interlocking with the rotation of the innermember as the kelly bar rotates while the inner member is in a state inwhich it is lifted to a certain extent relative to the second member andthe outer member, i.e., in a state in which the grab bucket is in theprocess of becoming closed, an underground obstacle clamped at the grabbucket can be rotated to more easily remove the underground obstaclecompared to the related art.

[0019] (2) It is desirable that excavating tool for an earth drillaccording to the present invention include the locking element at thetop of the inner member formed as a cylindrical portion, that thelocking element include a projecting portion projecting outward as anintegrated part of a disk having a diameter larger than the diameter ofthe cylindrical portion and that the locking element bearing plate beconstituted of a plate having a locking element passing portion which issubstantially isomorphic with the locking element and slightly largerthan the locking element.

[0020] By constituting the locking element and the locking elementbearing plate with plates larger than the cylindrical portion asdescribed above, the locking element and the locking element bearingplate are placed in contact with each other over a large area when theyare in a locked state so as to withstand a large load.

[0021] (3) In addition, it is desirable that the inner member in theexcavating tool for an earth drill according to the present inventioninclude a cylindrical portion the outer circumferential surface of whichcomes in contact with the guide rails located at a corner of an angulartube portion within the second member and bracing rails provided at theinner surfaces of the angular tube portion.

[0022] By placing the outer circumferential surface of the cylindricalinner member in contact with the guide rails and the bracing rails asdescribed above, the inner member does not become off-centered relativeto the second member or the outer member so as to ensure that thelocking element is allowed to pass through the locking element passingportion of the locking element bearing plate smoothly.

[0023] (4) It is also desirable that the excavating tool for an earthdrill according to the present invention further include third hydrauliccylinders that match the volumes of supply/discharge oil quantitiesbetween the first hydraulic cylinder and the second hydraulic cylinders.By providing the third hydraulic cylinders as a dummy cylinders, itbecomes unnecessary to mount an accumulator and the like at theexcavating tool and, at the same time, a structure having the bottomchambers of the hydraulic cylinders turned upward can be adopted. As aresult, the closed hydraulic circuit can be formed by using hydraulicpiping constituted of steel instead of hydraulic hose.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a side elevation of an earth drill having an excavatingtool as achieved in an embodiment of the present invention;

[0025]FIG. 2 is a side elevation of the excavating tool in FIG. 1 in itsmost contracted state;

[0026]FIG. 3 is a cross-section of a side elevation of the excavatingtool in FIG. 2 in its most extended state;

[0027]FIG. 4 is a plan view of the top of the excavating tool in FIG. 2;

[0028]FIG. 5 is a plan view of the top of the excavating tool in FIG. 3;

[0029]FIG. 6 is a sectional view taken along E-E in FIG. 2;

[0030]FIG. 7 shows the structures of the hydraulic cylindersconstituting an grab drive device for the grab bucket achieved in theembodiment;

[0031]FIG. 8 is a side elevation of the outer member achieved in theembodiment;

[0032]FIG. 9 is a front view of the outer member in FIG. 8;

[0033]FIG. 10 is a plan view of the top of the outer member achieved inthe embodiment;

[0034]FIGS. 11 and 12 present sectional views taken along F-F and G-Grespectively in FIG. 8;

[0035]FIG. 13 is a front view of the second member achieved in theembodiment;

[0036]FIG. 14 is a bottom view of the second member in FIG. 13;

[0037]FIG. 15 is a side elevation of the second member achieved in theembodiment;

[0038]FIG. 16 is a sectional view taken along D-D in FIG. 15;

[0039]FIG. 17 is a plan view of the first member constituting the innermember achieved in the embodiment;

[0040]FIG. 18 is a cutaway side elevation of the first member shown inFIG. 17;

[0041]FIG. 19 is a sectional view taken along H-H in FIG. 18;

[0042]FIG. 20 is a plan view of the second member constituting the innermember in the embodiment;

[0043]FIG. 21 is a side elevation of the second member shown in FIG. 20;

[0044]FIG. 22 is a bottom view of FIG. 20;

[0045]FIG. 23 is a side elevation of a structure that allows the innermember and the second member to be set in combination with each otherduring a forward rotation when the excavating tool in the embodiment isin the most contracted state;

[0046]FIG. 24 is a sectional view taken along I-I in FIG. 23;

[0047]FIG. 25 is a side elevation of a structure that allows the innermember and the second member to be set in combination with each otherduring a reverse rotation when the excavating tool in the embodiment isin the most contracted state;

[0048]FIG. 26 is a sectional view taken along J-J in FIG. 25;

[0049]FIG. 27 is a side elevation of a structure that allows the innermember and the second member to be set in combination with each otherwhen the grab bucket is in a half closed state in the excavating tool inthe embodiment; and

[0050]FIG. 28 is a sectional view taken along K-K in FIG. 27.

BEST MODE FOR CARRYING OUT THE INVENTION

[0051]FIG. 1 is a side elevation of an earth drill having the excavatingtool according to the present invention as achieved in an embodiment. Asshown in FIG. 1, a boom 51 is mounted at an earth drill main unit 50 soas to be freely raised or lowered with hoisting gear 52 and a frontframe 53 is mounted at the front of the earth drill main unit 50 so asto be freely raised and lowered with the hoisting gear 54. At the top ofthe front frame 53, a kelly drive device 56 that rotates a kelly bar 1inserted through the kelly drive device 56 so as to allow the kelly barto move up/down is installed. The kelly bar 1 is supported via a swiveljoint 59 with a hoisting rope 58 which is taken up and fed by a hoistwinch 57 mounted at the earth drill main unit 50. The kelly bar 1 isconstituted by fitting together three or more pipes of various sizes soas to allow them to move up/down but disallow their rotation relative toeach other, with a drilling bucket linked to the innermost pipe.Reference numeral 2 indicates the excavating tool according to thepresent invention, which is detachably mounted at the kelly bar 1 forbarrier excavation instead of the drilling bucket that is normallymounted at the kelly bar 1.

[0052]FIG. 2 is a side elevation of the excavating tool 2 in its mostcontracted state, i.e., in a state in which the grab bucket is open,FIG. 3 is a cross section of a side elevation of the excavating tool 2in its most extended state, i.e., in a state in which the grab bucket isclosed, FIGS. 4 and 5 are plan views of the top sides of FIGS. 2 and 3respectively, FIG. 6 is a sectional view taken along E-E in FIG. 2 andFIG. 7 shows the structure of the hydraulic cylinders constituting angrab drive device for the grab bucket.

[0053] In FIGS. 2 to 7, reference numeral 3 indicates an inner memberwhich is detachably connected to the kelly bar 1 with a pin 4 (see FIG.1), reference numeral 5 indicates a second member which is fitted on theouter side of the inner member 3 so as to be allowed to move up/downfreely and reference numeral 6 indicates an outer member which is fittedon the outer side of the second member so as to be allowed to moveup/down freely. A cylindrical bucket 7 is mounted at the outer member 6and the grab bucket 8 is mounted inside the cylindrical bucket 7.

[0054]FIG. 8 is a side elevation of the outer member 6, FIG. 9 is afront view of the outer member 6, FIG. 10 is a plan view of the top sideof the outer member 6 and FIGS. 11 and 12 are sectional views takenalong F-F and G-G in FIG. 8 respectively.

[0055] As shown in FIGS. 8, 9 and 11, the outer member 6 includes anangular tube portion 6 i having part of its side surface removed andlocated at the center of the outer member 6. At the front and rearsurfaces of the angular cube portion 6 i, mounting plates 6 a eachconstituted of a parallel plate are bonded and the cylindrical bucket 7is bonded to the lower portions of the mounting plates 6 a. As shown inFIGS. 2 and 3, a plurality of cutting teeth 7 a are disposed along thecircumferential direction at the lower portion of the cylindrical bucket7.

[0056] As shown in FIGS. 2 and 3, a first hydraulic cylinder 9 is housedinside the inner member 3, the piston rod of the first hydrauliccylinder 9 is connected to the inner member 3 with a pin 10 and thebottom side of the first hydraulic cylinder 9 is connected to the secondmember 5 with a pin 11.

[0057]FIG. 13 is a front view of the second member 5, FIG. 14 is abottom view of the second member 5, FIG. 15 is a side elevation of thesecond member 5 and FIG. 16 is a plan view of the second member 5. InFIGS. 13 to 15, reference numeral 5 n indicates an angular tube portionprovided at the center of the second member 5, which is fitted insidethe angular tube portion 6 i of the outer member 6 so as to be allowedto move up/down without allowing the angular tube portions 6 i to rotaterelative to each other. Reference numeral 5 a indicates a pin holeformed at the second member 5 at which the pin 11 is inserted. As theinner member 3 is lifted together with the kelly bar 1, the firsthydraulic cylinder 9 extends by stretching relative to the second member5 and, as a result, pressure oil is supplied to second hydrauliccylinders 12 provided to grab the grab bucket 8.

[0058] The second hydraulic cylinders 12 are mounted at brackets 5 b(see FIGS. 13 to 15) provided to the front and to the rear of theangular tube portion 5 n of the second member 5 and at brackets 6 j (seeFIG. 12) provided at the cylindrical bucket mounting parallel plates 6 alocated to the front and to the rear of the outer member 6 via pins 13and 14 respectively. Reference numeral 5 c in FIGS. 13 to 15 andreference numeral 6 c in FIGS. 8 and 12 respectively indicate pin holesat which the pins 13 and 14 are inserted.

[0059] As shown in FIGS. 13 to 15, mounting plates 5 d are bonded to theleft and right sides of the angular tube portion 5 n at the secondmember 5. Brackets 5 f are mounted at the front ends of these mountingplates 5 a*[1]. Each bracket 5 f includes pin hole 5 e through which apin 15 (see FIGS. 2 and 3) is inserted to rotatably connect a pivotalconnecting portion located on the upper inner side of a jaw 8 a of thegrab bucket 8.

[0060] As shown in FIGS. 2 and 3, each bracket 6 b at the outer member 6and the central portion of the corresponding jaw 8 a are rotatablylinked via links 16 and pins 17 and 19. Reference numeral 6 d in FIGS.8, 9 and 12 indicates a pin hole through which the pin 17 is inserted.

[0061] As shown in FIG. 7, third hydraulic cylinders 20 are provided onone side of the hydraulic circuit between the first hydraulic cylinders9 and the second hydraulic cylinders 12. The third hydraulic cylinders20 constitute a dummy hydraulic cylinder having the function of matchingthe supply/discharge oil quantities between the hydraulic cylinders 9and 12. The presence of such third hydraulic cylinders 20 eliminates theneed to mount an accumulator and the like at the excavating tool. Inaddition, since a structure having the piston rod side of the firsthydraulic cylinder 9 turned upward and the bottom chambers of the secondhydraulic cylinders 12 turned upward can be adopted, a closed hydrauliccircuit can be formed with hydraulic piping constituted of steel insteadof hydraulic hose. As shown in FIGS. 2, 4, 5, 8, 9 and 11, the thirdhydraulic cylinders 20 are mounted by pinning their upper ends tobrackets 6 h provided at ribs 6 e constituted of parallel plates at theouter member 6.

[0062] As shown in FIG. 6, the inner member 3 is constituted of a firstmember 3A and a second member 3B. FIGS. 17 through 19 shows the firstmember 3A which includes a locking element 3 d assuming the shape of adisk larger than a cylindrical portion 3 c and located above thecylindrical portion 3 c. The locking element 3 d includes a plurality ofprojecting portions 3 e projecting outward and formed along the outercircumference. The first member 3A also includes a connecting portion 3f assuming an angular tube shape, which connects with the kelly bar 1and is located above the locking element 3 d, and a pin hole 3 g throughwhich the pin 4 is inserted to mount the first member 3A at the kellybar 1 is formed at the connecting portion 3 f.

[0063]FIGS. 20 through 22 show the second member 3B which includes alocking element 3 j isomorphic with the locking element 3 d, havingprojecting portions 3 i similar to those of the locking element 3 d,assuming the shape of a disk with an area larger than the area of acylindrical portion 3 h and located at the top of the cylindricalportion 3 h. In addition, inside the cylindrical portion 3 h, acylindrical element 23, which supports a connecting piece 22 of the pin10 at the first hydraulic cylinder 9 is fastened. As shown in FIGS. 3and 6, the first member 3A and the second member 3B are fastened to eachother with a fastening piece 24 by fitting their cylindrical portions 3c and 3 h with each other. In addition, as shown in FIGS. 2 through 5,the locking elements 3 d and 3 j are fastened to each other with afastening piece 25 by placing each projecting portion 3 e in alignmentwith a projecting portion 3 i.

[0064] As shown in FIGS. 21 and 22, at the bottom of the second member3B, projections 3 k are provided at two positions facing opposite eachother. As shown in FIGS. 23 and 24, at the angular tube portion 5 n ofthe second member 5, guide rails 5 j extending along the longitudinaldirection and each constituted of two rods 5 h and 5 i are provided intwo corners facing opposite each other. In addition, at the innersurface of the angular tube portion 5 n of the second member 5, bracingrails 5 p which, together with the guide rails 5 j, come in contact withthe outer circumferential surface of the cylindrical portion 3 h of theinner member 3 are provided. At two side surfaces of the second member 5facing opposite each other, openings 5 k at which the projections 3 kare fitted are provided, with stoppers 5 m provided along the edges ofthe openings 5 k. As shown in FIG. 23, of the two rods 5 h and 5 iconstituting guide rails 5 j, the lower end of the rod 5 h locatedcloser to the opening 5 k is set at a height H1 substantially level withthe upper side of the opening 5 k, whereas the lower end of the rod 5 ilocated further away from the opening 5 k is set at a height H2substantially level with the lower side of the opening 5 k.

[0065] As shown in FIGS. 4, 5 and 10, at the top of the outer member 6,a locking element bearing plate 6 fconstituted of a plate having alocking element passing portion 6 gsubstantially isomorphic with thelocking elements 3 g and 3 j of the inner member and slightly largerthan the locking elements 3 d and 3 j is provided. The locking elementpassing portion 6 gincludes dented portions 6 j (may be grooves) incorrespondence to the projecting portions 3 e and 3 i mentioned earlier.When the projections 3 k of the inner member 3 fitted at the guide rails5 j, the projecting portions 3 e and 3 i of the locking elements 3 d and3 j are set at positions corresponding to the positions of the dentedportions 6 j of the locking element passing portion 6 g, as shown inFIG. 5, and thus, the locking elements 3 d and 3 j are allowed to passthrough the locking element passing portion 6 g. Since the outercircumferential surface of the cylindrical portion 3 h of the innermember 3 is placed in contact with the guide rails 5 j and the bracingrails 5 p, the inner member 3 does not become off-centered relative tothe second member 5 and the outer member 6, and as a result, the lockingelements 3 d and 3 j are allowed to pass through the locking elementpassing portion 6 gsmoothly without play.

[0066] When the inner member 3 is at the lowest position relative to theouter member 6, i.e., when the excavating tool is in the most contractedstate, the projections 3 k of the inner member 3 are set lower than thebottom ends of the rods 5 h, as shown in FIG. 23, and thus, as the innermember 3 is caused to rotate forward together with the kelly bar 1 (asthe inner member 3 rotates along the excavating direction), the innermember 3 rotates forward relative to the second member 5 and the outermember 6, thereby allowing the projections 3 k to slip out of theopenings 5 k to come in contact with the stoppers 5 m. As the innermember 3 is made to rotate forward in this manner, the projectingportions 3 e and 3 i of the locking elements 3 d and 3 j become lockedat the locking element bearing plate 6 f as shown in FIG. 4, and thus,the outer member 6 can be lifted together with the inner member 3 bylifting the kelly bar 1. By constituting the locking elements 3 d and 3j and the locking element bearing plate 6 fwith plates larger in sizethan the cylindrical portions 3 c and 3 h in the structure, the lockingelements 3 d and 3 j locked at the locking element bearing plate 6 fareallowed to achieve contact with the locking element bearing plate 6fover large areas so as to withstand a large load.

[0067] Next, the operation of the excavating tool is explained. Afterthe soil is discharged overground, the grab bucket 8 is in an openstate, and as the kelly bar 1 is rotated forward with the cylindricalbucket 7 set on the ground in this state, the locking elements 3 d and 3j become locked at the locking element bearing plate 6 f as shown inFIG. 4. The excavating tool 2 is then hoisted into the bore hole 30 (seeFIG. 1).

[0068] As the cylindrical bucket 7 of the excavating tool 2 is set ontothe bottom surface of the bore hole 30, the kelly drive device 56 isactivated to rotate the excavating tool 2 along the forward directionvia the kelly bar 1. As a result, the projections 3 k of the innermember 3 come into contact with the stoppers 5 m of the second member 5.In addition, the projecting portions 3 e and 3 i of the locking.elements 3 d and 3 j become locked at the locking element bearing plate6 fof the outer member 6. The rotational force of the kelly bar 1 iscommunicated to the cylindrical bucket 7 in this state, thereby causingthe cylindrical bucket 7 to rotate and allowing the cylindrical bucket 7to excavate a slab, cobblestones or boulders.

[0069] Such an excavating operation can be executed with a load smallerthan the load of the excavating tool 2 applied to the excavating surfaceby operating the hoist winch 57 slightly along the lifting direction toapply a slight force to the kelly bar 1 along the lifting direction andthus rotating the kelly bar 1 along the forward direction, i.e., alongthe excavating direction. As a result, even when the excavatingoperation is executed by rotationally driving a relatively largeexcavating tool 2 with a small earth drill, the operation can beexecuted with a small pressing force. Thus, a sufficient drive force isassured in the excavating operation. In addition, even if there is anexcessively large excavating reactive force, the excavating operationcan be executed with an optimal pressing force. It goes without sayingthat depending upon the situation, the excavating operation can beexecuted with a pressing force equal to or greater than the load of theexcavating tool 2 and the like by holding the kelly bar 1 downward witha pressing device (not shown) provided at the kelly drive device 56.

[0070] As the excavating operation executed with the cylindrical bucket7 progresses and excavated material is collected in the cylindricalbucket 7 in a quantity suitable to be taken into the grab bucket 8, theinner member 3 is rotated in reverse together with the kelly bar 1. Thisreverse rotation places the projections 3 k of the inner member 3 eachin contact with one of the rods, i.e., the 5 rod 5 i constituting aguide rail 5 j, as shown in FIGS. 25 and 26.

[0071] Then, the inner member 3 is lifted together with the kelly bar 1in the state shown in FIGS. 25 and 26. In this situation, since theloads of the outer member 6, the cylindrical bucket 7 and the grabbucket 8 are applied to the second member 5, the first hydrauliccylinder 9 is first allowed to extend. As the first hydraulic cylinder 9extends as described above, the oil in a rod chamber a of the firsthydraulic cylinder 9 becomes pressurized to become pressure oil whichthen enters bottom chambers b at the tops of the second hydrauliccylinders 12, as indicated by the arrows in FIG. 7. In addition, the oilin rod chambers c of the second hydraulic cylinders 12 enters rodchambers d of the third hydraulic cylinders 20, whereas the oil in thebottom chambers e of the third hydraulic cylinders 20 enters a bottomchamber f of the first hydraulic cylinder 9.

[0072] As the oil flows as described above, the second hydrauliccylinders 12 extend, which causes the second member 5 to move upward. Asa result, the opposite ends of the jaws 8 a connected via the pins 15with the brackets 5 f fastened to the second member 5 become lifted,thereby closing the grab bucket 8, as shown in FIG. 3 to allow it tograb the excavated material. It is to be noted that if a slab is beingexcavated, the grab bucket 8 grabs the slab drilled in a disk shape atits edge, and thus, the grab bucket 8 does not close as completely.

[0073] As described above, the force with which the kelly bar 1 islifted can be used to close the grab bucket 8 and, as a result, a highlevel of closing force can be obtained by using the hoisting force ofthe hoist winch 57.

[0074] In this structure, the second hydraulic cylinders 12 and thethird hydraulic cylinders 20 function as a booster that compensates forthe difference between the supply and discharge quantities of oilattributable to the difference in the sectional areas of the rod chambera and the bottom chamber f of the first hydraulic cylinder 9. Thus, aclosed circuit can be constituted without having to employ anaccumulator.

[0075] After the excavated material is grabbed in the grab bucket 8 asdescribed above, the kelly bar 1 is lifted together with the excavatingtool 2 by the hoist winch 57. After the excavating tool 2 having beenlifted to the ground level is set on the ground surface, the kelly bar 1is lowered to allow the oil to flow in the direction opposite from thatindicated by the arrows in FIG. 7, thereby causing the first hydrauliccylinder 9 to contract, as shown in FIG. 2. As a result, the secondhydraulic cylinders 12 also contract to open the grab bucket 8 todischarge the excavated material in the grab bucket 8.

[0076] During the operation described above, if the lifting reactiveforce generated at the bottom of the bore hole is too large relative tothe force applied to close the grab bucket 8, the grab bucket 8 can belifted in an open state by lowering the inner member 3 again, rotatingthe kelly bar forward by a specific angle and locking the lockingelements 3 d and 3 j at the locking element bearing plate 6 f. Thus, theexcavating tool can be lifted from underground even under suchcircumstances.

[0077] Also, as shown in FIGS. 27 and 28, when the inner member 3 islifted to a certain extent relative to the second member 5 and the outermember 6, i.e., when the grab bucket 8 is undergoing the process ofbecoming closed, the projections 3 k of the inner member 3 are clampedbetween the rods 5 h and 5 i of the guide rails 5 j. If the inner member3 is rotated together with the kelly bar 1 in this state, the secondmember 5 and the outer member 6, too, can be rotated forward and back byinterlocking with the rotation of the inner member 3. Thus, by rotatingthem while an underground obstacle is held in the grab bucket 8, theunderground obstacle can be handled with greater ease than in therelated art.

[0078] The present invention may also be adopted in a structure having acylindrical add-on excavating tool with cutting teeth, which isdetachably mounted at the lower end of the cylindrical bucket 7 with afastening piece such as a bolt, as described in Japanese UnexaminedPatent Publication No. 2001-90465. By adopting the structure, it becomespossible to execute the excavating operation in an optimal manner at alltimes by selecting an excavating tool having an optimal depth and anoptimal function for a given excavating site from various add-onexcavating tools with varying heights and varying types of cuttingteeth.

[0079] In addition, the present invention may be implemented without thethird hydraulic cylinders 20 by, for instance, reversing the top sideand the bottom side of the second hydraulic cylinders 12. Also, thepresent invention may be adopted in an earth drill having a structure inwhich the kelly drive device is moved up/down along a leader. Moreover,the inner member 3 may have a single cylinder structure instead of thedouble cylinder structure.

INDUSTRIAL APPLICABILITY

[0080] The excavating tool for an earth drill according to the presentinvention, having a grab bucket provided inside a cylindrical bucket andthe grab bucket is caused to close by the force with which the kelly baris lifted, allows the locking elements of the inner member to be lockedat the locking element bearing plate of the outer member while theexcavating tool is in its most contracted state. As a result, anexcavating operation can be executed while a load smaller than the loadof the excavating tool is applied. Thus, an earth drill with a smalldrive force is able to perform an excavating operation with a relativelylarge bucket. In addition, whenever the situation calls for it, an idealexcavating operation can be executed with a small pressing force. Sinceit adopts the structure having the guide rails at the second member atwhich the projections formed at the outer circumference of the innermember become held so as to be allowed to move up/down freely, it ispossible to rotate the grab bucket while it is closed to a certainextent, and consequently, underground obstacles can be removed with easein a manner appropriate to a given situation.

1. An excavating tool for an earth drill, characterized in that;comprising a tubular inner member (3) connected to a kelly bar (1), atubular second member (5) fitted on the outer side of said inner member(3) so as to be allowed to move up/down freely and an outer member (6)fitted on the outer side of said second member (5) so as to be allowedto move up/down freely: a cylindrical bucket (7) and a grab bucket (8)housed in side said cylindrical bucket (7) are mounted at said outermember (6); a first hydraulic cylinder (9) is mounted between said innermember (3) and said second member (5), and second hydraulic cylinders(12) which are caused to extend/contract by the pressure oil from saidfirst hydraulic cylinder (9) are mounted between said second member (5)and jaws (8 a) of said grab bucket (8); a locking mechanism is providedbetween said inner member (3) and said outer member (6), said lockingmechanism is constituted of locking elements (3 d, 3 j) provided at theouter circumference of said inner member (3) and a locking elementbearing plate (6 f) provided at the upper portion of said outer member(6), said locking elements (3 d, 3 j) are allowed to pass through saidlocking element bearing plate (6 f) when said inner member (3) and saidouter member (6) achieve a specific relative rotational angle and saidlocking elements (3 d, 3 j) become locked at said locking elementbearing plate (6 f) to disallow relative vertical movement of said innermember (3) and said outer member (6) by rotating said inner member (3)forward when said excavating tool (2) is in a most contracted state; andprojections (3 k) provided at the outer circumference of said innermember (3) are fitted at guide rails (5 j) extending along thelongitudinal direction at the inner circumference of said second member(5) so as to be allowed to move up/down freely, and said inner member(3) is allowed to rotate forward relative to said second member (5)within a predetermined range when said excavating tool (2) is in themost contracted state.
 2. An excavating tool (2) for an earth drillaccording to claim 1, characterized in that: said inner member (3)includes said locking elements (3 d, 3 j) above cylindrical portions (3c, 3 h); said locking elements (3 d, 3 j) respectively includeprojecting portions (3 e, 3 i) projecting outward as integrated portionsof disks having diameters larger than the diameters of said cylindricalportions (3 c, 3 h); and said locking element bearing plate (6 f) isconstituted of a plate having a locking element passing portion (6 g)substantially isomorphic with said locking elements (3 d, 3 j) andslightly larger than said locking elements (3 d, 3 j).
 3. An excavatingtool (2) for an earth drill according to claim 1 or 2, characterized inthat: said inner member (3) includes a cylindrical portion (3 h); andthe outer circumferential surface of said cylindrical portion (3 h) isin contact with said guide rails (5 j) provided at corners of an angulartube portion (5 n) inside said second member (5) and bracing rails (5 p)provided at the inner surface of said angular tube portion (5 n).
 4. Anexcavating tool (2) for an earth drill according to any of claims 1through 3, characterized in that: third hydraulic cylinders (20) thatmatch supply/discharge oil quantities between said first hydrauliccylinder (9) and said second hydraulic cylinders (12) are provided in aclosed hydraulic circuit located between said first hydraulic cylinder(9) and said second hydraulic cylinders (12).